1. Field of the Invention
The present invention broadly relates to high power flowing gas lasers and chemical processing devices and, more particularly, is concerned with the improvement of the electrical efficiency thereof by controlling separately the conductivity of each layer of a multilayer gas flow serving as the sustainer discharge electrodes and the lasing or chemical processing medium.
2. Description of the Prior Art
One form of high power laser employs a lasing gas flow which is perpendicular to both the electrical discharge axis and the optical axis of the laser. This gives rise to a transverse flow configuration, the principal advantage of which being that the lasing gas dwell time in the optical cavity is much shorter than with lasers of other configurations, such as axial flow devices. The result is a laser having the possibility of much higher power density and consequently much more power per unit length of optical cavity.
In such a laser, the lasing gas flow is preionized by an electron beam to make it electrically conducting and thereafter a main, or sustainer, electrical discharge is delivered independently to this conducting region of the gas between two electrodes at a voltage less than the breakdown potential of the lasing gas. Theoretically, an electric discharge should result which is uniform and free of filaments or arcing.
In one embodiment of this transverse flow configuration, such as shown schematically in FIG. 5 of U.S. Pat. No. 3,702,973, the gas ionization is accomplished through use of a large area, low power electron beam which irradiates the optical cavity of the laser. The E-beam is fired perpendicular to both the direction of gas flow and the optical axis. The electrical sustainer discharge is, therefore, in the same direction as the E-beam.
The E-beam/sustainer discharge technique for pumping high power lasers, as just described, has been found to work well for may gas mixtures, and may be used for electrical initiation of high power chemical lasers as well. However, the output power of lasers utilizing this technique is limited by the breakdown of the lasing medium. In other words, an upper limit to the power in the outputted laser beam is imposed by the voltage at which the lasing gas begins to break down. The breakdown appears to be caused by electric field concentration at the cathode screen or rods structure, resulting in formation of streamers across the discharge electrodes.
The consequence of greater likelihood of gas breakdown as the electric discharge field is increased is unfortunate because it has been found that in many laser applications the electrical efficiency increases sharply at higher E/p ratios (electric field to gas pressure). For instance, when using a fluorine gas mixture it was found that arcing occurs with an applied electric field at only 60 percent of the breakdown strength of the gas mixture.
Besides increasing electrical efficiency, an increased electric field is highly desirable in some laser applications to increase energy density and reduce device dimensions. Furthermore, some lasing gas mixtures may only be made to work at an electric field close to their breakdown potentials. Therefore, a need exists to develop a technique to achieve a higher controlled sustainer electric field discharge operation without deleteriously affecting the lasing medium.